RC Oscillator Circuit With Switched Capacitance for Frequency Stability
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Solution Overview
Problem
RC oscillators in integrated circuits face instability due to temperature variations and dependency on operation voltage, affecting the frequency of the output signal.
Innovation Solution
The oscillator design includes a resistance unit with a positive and negative temperature coefficient resistor, and a capacitance unit with capacitors that adjust their connection based on control signals, reducing frequency variation by adjusting equivalent capacitance and using specific transistor ratios to minimize frequency changes with voltage drift.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Volume of moving object
If RC oscillators are implemented in integrated circuits to save layout space, then device volume is reduced, but frequency stability deteriorates due to temperature variations affecting resistance values
Solution Approach 1:
The patent uses a positive temperature coefficient resistor and a negative temperature coefficient resistor in series to create a resistance unit whose total resistance remains stable across temperature variations. The positive temperature coefficient resistor increases resistance with temperature while the negative temperature coefficient resistor decreases resistance with temperature, compensating for each other's effects and maintaining frequency stability in the integrated circuit oscillator.
2Adaptability or versatility
If the oscillating frequency is made dependent on operation voltage for control flexibility, then adaptability is improved, but frequency stability deteriorates as voltage changes cause frequency drift
Solution Approach 1:
The patent employs a capacitance unit with multiple capacitors that can be selectively connected or disconnected based on control signals. By changing the effective capacitance value in response to voltage variations, the circuit compensates for frequency drift caused by voltage changes, thereby maintaining frequency stability while preserving control flexibility through the selective capacitor switching mechanism.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The design achieves stable oscillating frequency across varying temperatures and operation voltages, with frequency deviations less than 2 kHz over a significant temperature range and voltage variation, enhancing system stability.
Implementation Method 1
The capacitance unit includes a plurality of capacitors. One terminal of each of the capacitors is coupled to the output point, and the other terminal of each of the capacitors is coupled to the first reference point or a reference ground according to a control signal.
Implementation Method 2
The resistance unit with a positive and negative temperature coefficient resistor
Data Source
AI summary
An oscillator is provided and includes a resistance unit, a capacitance unit, a first inverter and a second inverter. The resistance unit is serially connected between a first reference point and a second reference point. The capacitance unit is coupled between the first reference point and an output point, and includes capacitors. One terminal of each of the capacitors is coupled to the output point, and the other terminal of each of the capacitors is coupled to the first reference point or a reference ground according to a control signal. The input terminal of the first inverter is coupled to the first reference point, and the output terminal of the first inverter is coupled to the second reference point. The input terminal of the second inverter is coupled to the output terminal of the first inverter, and the output terminal of the second inverter is coupled to the output point.